A Heavy Heart: Depression and Cardiac Function

Two recently published studies have found that changes in heart function are seen during major depression [1] and also seen in some people who have recovered from depression [2]. This link between mental health and physical health emphasises how the body and mind are linked. Furthermore, it also suggests that some people with depression may be at increased risk of cardiac disease. The research also sheds further light on the biological pathways of depression.

Depression is common: in the US 1 in 10 adults report depression [3] and in Europe affects women twice as often as men with approximately one in 6 women experiencing depression in their lifetime [4]. The World Health Organisation predicts that depression will be the leading cause of disability in high income countries by 2030 [5]. The word “depression” has fallen into common parlance, but it properly used to describe a disorder in low mood. Although there are various subtypes, “depression” is commonly used to refer to “Major depressive disorder” which is defined in the “Diagnostic Statistical Manual of Mental Disorders” or “DSM”. The DSM sets out criteria for mental health conditions and states that major depressive disorder is characterised by a mix of the following symptoms present most of the time for at least two weeks [6]:

depressed mood most of the day, nearly every day

decreased interest or pleasure

changes in weight

changes in sleep pattern

fatigue

feelings of worthlessness or guilt

reduced ability to concentrate or make decisions

thoughts of death and/or suicide

The autonomic nervous system controls much of our involuntary functions, regulating breathing, dilation of blood vessels and heart rate. It is divided into two systems: sympathetic and parasympathetic, which is based on which nerves each system works with. The parasympathetic system is involved in cardiac regulation, being key in regulating the “vagus nerve” which can lower heart rate. Previous research had found there may be issues with heart rate variability and therefore the degree to which the autonomic cardiac (heart) system is working in people with depression [7].

Chang and colleagues set out to complete two studies that had enough participants in their samples to enable them to make statistically valid conclusions. Both studies used a similar method. Participants were selected who in two groups of those who had a history of depression but not using medication and those with no history. All participants were not smoking nor did any have major health conditions including hypertension or cardiacarrhythmia. Depression was measured using questionnaires (the Hamilton Depression Scale and the Beck Depression Inventory). Heart rate variability was used as an indicator of how well the autonomic nervous system is regulating cardiac function. This was measured using electrocardiogram to measure electrical nerve impulses across the heart.

In their first study, Chang and colleagues found that heart rate variability was correlated with measures of depression severity [1]. Participants with major depression had lower heart rate variability than those without depression. Those with more severe depression had a more reduced variability in their heart rate. The largest relationship (a correlation of 0.72, which is classed as large) was between suicide measures and heart rate variability, and the relationship between heart rate variability and insomnia, anxiety and physical symptoms of depression were also significant. The system involved appears to be the parasympathetic system. In their second study, Chang and colleagues focused on people with fully remitted major depression — meaning people had experienced major depression in the past but symptoms were no longer present [2]. They found that generally speaking, those with remitted major depression showed no difference in their heart rate variability when compared to those with no history of depression. However, when they looked into this in more detail, they revealed difference based on whether people had experienced significant thoughts about suicide. They found that people who had experienced suicidal thoughts during their depression but were no longer depressed had significantly reduced heart-rate variability. This was true when compared to both healthy controls and those with remitted major depression who had not had significant thoughts about suicide. The impact of having suicidal ideation in the past appears to be associated to ongoing differences in autonomic nervous system function.

Reduced heart rate variation seems to be a physiological marker of major depression. However, the usefulness of this finding alone is limited — depression will still need to be diagnosed using systematic interviews and questionnaire measures, not least as heart rate variability may signal other health conditions also. There appears therefore to be something significant about suicidal thinking. Both studies found that suicidal thinking was linked to reduced heart rate variability. Research has found a link between parasympathetic nervous system activity and regulation of emotions, including how impulsive people are. The studies suggest that suicidal thinking is related to changes in autonomic system regulation. We do not yet know exactly how or why or whether the thoughts cause the changes or vice versa. It may be that there are behaviours such as reduced intake of food and water in people with suicidal thinking (depression is often linked to reduced self-care) that underlies this difference [8]. Another idea, put forward by the authors of these papers, is the role of serotonin, a neurotransmitter. The idea is that lowered serotonin is associated to lower heart rate variability and lowered serotonin is commonly thought to be associated also to depression. Indeed, many antidepressant drugs work by acting on serotonin.

These studies have three main messages. First, we often think of physical health and mental health as two separate things. These studies emphasise the link between the two. The nervous system regulates our physical systems and of course it includes the brain — connecting the mind and body in a very overt way. Second, the studies suggest that suicidal thinking is related to changes in autonomic system regulation. Suicidal thinking is not only a serious risk to quality of life, a serious risk to actually attempting and completing suicide, requiring serious attention and intervention to support the person. It appears now suicidal thinking is also a longer term risk to cardiac function and should therefore also be taken seriously by medical doctors. The stigma around depression and suicide needs to be reduced to ensure people get the help they need, for both the psychological and physical impacts of depression. Third, current major depression or remitted major depression that was characterised by thoughts of suicide represent risk factors for cardiac disease. If you have either, remind you physician to monitor your heart health and take care to try to live as healthy as lifestyle as possible, getting support as required to manage depression and its consequences.

Faith Martin, Ph.D., is a PhD-trained research psychologist. Faith is currently studying health and lifestyle interventions at the University of Bath in the United Kingdom. Her research interests include quality of life measurement, promotion of self-management, intervention development and cross-cultural psychology.